The Universal Mobile Telecommunications System (UMTS) is a third generation mobile cellular system for networks based on the GSM standard. UMTS specifies a complete network system including the radio access network (UMTS Terrestrial Radio Access Network (UTRAN). A fourth generation Evolved Packet System (EPS) architecture specified by 3rd Generation Partnership Project (3GPP) standard, also sometimes referred to as a “Long Term Evolution (LTE) EPS architecture” (or simply as “LTE” or “4G”), now has a Release 12 that provides a way for User Equipment (UE) to be connected to two Evolved UTRAN (E-UTRAN) NodeBs (eNBs) at the same time using “Dual Connectivity” (DC). An eNB is a radio access point, implemented largely in hardware, connected to the mobile phone network that communicates directly with mobile handsets (also referred to as “user equipment” or “UEs”), like a base transceiver station (BTS) in Global System for Mobile Communications (GSM) networks. In LTE DC, there is a Master eNB (MeNB) that maintains the Radio Resource Control (RRC) connection with the UE and there is a Secondary eNB (SeNB) without RRC. The user data traffic can flow via both the Master and the Secondary, thus justifying the name “dual connectivity.” Dual Connectivity advantageously allows dynamically distributing traffic between the Master and the Secondary radio access points, e.g. offloading traffic from the Master to the Secondary based on load-balancing considerations.
As described in 3GPP TS 36.300 Release 12, in LTE DC, the radio protocol architecture that a particular bearer uses depends on how the bearer is setup. Three bearer types exist: Master Cell Group (MCG) bearer, Secondary Cell Group (SCG) bearer and split bearer. The SCG bearer setup provides various advantages, such as e.g., ability to relax requirements for having an ideal X2 backhaul link, no buffering requirement on MeNB for packets transmitted by the SeNB, no flow control needed between MeNB and SeNB, local break-out and content caching at SeNB straightforward for dual connectivity UEs, etc. However, it also suffers from certain drawbacks. For example, one drawback is that offloading of traffic from MeNB to SeNB must be performed by a Mobile Management Entity (MME), which is an entity within a core network (CN) of a telecommunications system, and cannot be very dynamic. Another is that all switches between MeNB and SeNB involve signaling in the CN, taking up valuable limited bandwidth in CN communications. Improvements with respect to one or more of these drawbacks of the SCG would be desirable.